XML QUERY LANGUAGE Prepared by Prof. Zaniolo, Hung-chih Yang, Ling-Jyh Chen Modified by Fernando Farfán

Motivation  Increasing amounts of information stored, exchanged, and presented as XML.  Ability to intelligently query XML data sources.  XML strength: Flexibility representing many kinds of information from diverse sources.  XML query language must retrieve and interpret information from these diverse sources. 2 XML Query Language Tutorial

Desiderata for an XML Query Language  Expressive power  Semantics  Compositionality  Schema  Program manipulation 3 XML Query Language Tutorial

Different Query Languages for XML  XPath & XQL: path expression syntax suitable for hierarchical documents  XML-QL: binding variables and using bound variables to create new structures  SQL: SELECT-FROM-WHERE pattern for restructuring data  OQL: ODMG  Quilt: accept a lot of advantages from above XML query languages, and it’s the immediate ancestor of XQuery 4 XML Query Language Tutorial

What is XQuery 5 XML Query Language Tutorial

What is XQuery (cont.)  Designed to meet the requirements identified by the W3C XML Query Working Group  “XML Query 1.0 Requirements”  “XML Query Use Cases”.  Designed to be a small, easily implementable language.  Flexible enough to query a broad spectrum of XML sources (both databases and documents).  Defines a human-readable syntax for that language. 6 XML Query Language Tutorial

What is XQuery (cont.)  Expression: Basic building block.  Functional language (at least claimed by the spec.)  Strongly-typed language. 7 XML Query Language Tutorial

XQuery vs. XSLT Reinventing the Wheel?  XSLT is document-driven; XQuery is program driven.  XSLT is written in XML; XQuery is not.  An assertion (unproven): XSLT 2.0 can do everything XQuery can do. 8 XML Query Language Tutorial

XQuery Concepts  A query in XQuery is an expression that:  Reads a number of XML documents or fragments  Returns a sequence of well-formed XML fragments 9 XML Query Language Tutorial

The Principal Forms of XQuery Expressions  Primary  Literals, variables, function calls and parentheses (for control precedence).  Path  Locates nodes within a tree, and returns a sequence of distinct nodes in document order.  Sequence  An ordered collection of zero or more items, where an item may be an atomic value or a node.  An item is identical to a sequence of length one containing that item. Sequences are never nested. 10 XML Query Language Tutorial

The Principal Forms of XQuery Expressions (Cont.)  Arithmetic  Arithmetic operators for addition, subtraction, multiplication, division, and modulus.  Comparison  Four kinds of comparisons: value, general, node, and order comparisons.  Logical  A logical expression is either an AND-expression or an OR- expression.  The value of a logical expression is always a Boolean value. 11 XML Query Language Tutorial

The Principal Forms of XQuery Expressions (Cont.)  Constructor  Constructors can create XML structures within a query.  There are constructors for elements, attributes, CDATA sections, processing instructions, and comments.  FLWR  Expression for iteration and for binding variables to intermediate results.  Useful for computing joins between two or more documents and for restructuring data.  Pronounced "flower", stands for the keywords FOR, LET, WHERE, and RETURN, the four clauses found in a FLWR expression. 12 XML Query Language Tutorial

The Principal Forms of XQuery Expressions (Cont.)  Sorting expressions  Provides a way to control the order of items in a sequence.  Conditional expressions  Based on the keywords IF, THEN, and ELSE.  Quantified expressions  support existential and universal quantification.  The value of a quantified expression is always true or false. 13 XML Query Language Tutorial

The Principal Forms of XQuery Expressions (Cont.)  Data types  Runtime type checking and manipulation  Validate  A validate expression validates its argument with respect to the in-scope schema definitions, using the schema validation process described in XML Schema. 14 XML Query Language Tutorial

XQuery Example 1  Find all books with a price of $39.95 XQuery: document("bib.xml")/bib/book[price = 39.95] Result: Data on the Web Abiteboul Serge Buneman Peter Suciu Dan Morgan Kaufmann Publishers XML Query Language Tutorial

XQuery Example 2  Find the title of all books published before 1995 XQuery: < 1995]/title Result: TCP/IP Illustrated Advanced Programming in the Unix environment 16 XML Query Language Tutorial

XQuery Example 3 (For Loop)  List books published by Addison-Wesley after 1991, including their year and title. XQuery: { for $b in document("bib.xml")/bib/book where $b/publisher = "Addison-Wesley" and > 1991 return { $b/title } } 17 XML Query Language Tutorial

XQuery Example 3 (For Loop)  List books published by Addison-Wesley after 1991, including their year and title… Result: TCP/IP Illustrated Advanced Programming in the Unix environment 18 XML Query Language Tutorial

XQuery Example 4 (Join)  For each book found at both bn.com and amazon.com, list the title of the book and its price from each source. XQuery: { for $b in document("bib.xml")//book, $a in document("reviews.xml")//entry where $b/title = $a/title return { $b/title } { $a/price } { $b/price } } 19 XML Query Language Tutorial

XQuery Example 4 (Join)  For each book found at both bn.com and amazon.com, list the title of the book and its price from each source. Result: TCP/IP Illustrated Advanced Programming in the Unix environment Data on the Web XML Query Language Tutorial

XQuery Example 5 ( Grouping + quantifier )  For each author in the bibliography, list the author's name and the titles of all books by that author, grouped inside a "result" element. XQuery: { for $a in distinct-values(document("bib.com")//author) return { $a } { for $b in document(" where some $ba in $b/author satisfies deep-equal($ba,$a) return $b/title } } 21 XML Query Language Tutorial

XQuery Example 5 ( Grouping + quantifier )  For each author in the bibliography, list the author's name and the titles of all books by that author, grouped inside a "result" element. Result: Stevens W. TCP/IP Illustrated Advanced Programming in the Unix environment Abiteboul Serge Data on the Web …… 22 XML Query Language Tutorial

XQuery Example 6 (Sorting)  List the titles and years of all books published by Addison-Wesley after 1991, in alphabetic order. XQuery: { for $b in document(" where $b/publisher = "Addison-Wesley" and > 1991 return { } { $b/title } sortby (title) } 23 XML Query Language Tutorial

XQuery Example 6 (Sorting)  List the titles and years of all books published by Addison-Wesley after 1991, in alphabetic order. Result: Advanced Programming in the Unix environment TCP/IP Illustrated 24 XML Query Language Tutorial

XQuery Example 7 (Recursion)  Convert the sample document from "partlist" format to "parttree" format. XQuery: define function one_level (element $p) returns element { { for $s in document("partlist.xml")//part where = return one_level($s) } } { for $p in return one_level($p) } 25 XML Query Language Tutorial

XQuery Example 7 (Recursion)  Convert the sample document from "partlist" format to "parttree" format. Result: 26 XML Query Language Tutorial

XQuery Example 8 (Sequence)  In the Procedure section of Report1, what Instruments were used in the second Incision? XQuery: for $s in document("report1.xml")//section[section.title = "Procedure"] return ($s//incision)[2]/instrument Result: electrocautery 27 XML Query Language Tutorial

XQuery Support on RDBMSs XML Query Language Tutorial 28  Oracle XQuery Engine   Introduction to XQuery in SQL Server 2005  us/library/ms345122(SQL.90).aspx  Query DB2 XML data with XQuery  dm-0604saracco/  DataDirect: Data Integration Suite – MySQL Database Support  integration/datasources/databases/mysql/index.ssp

Conclusion  XQuery is a simple substitution of XSLT, JSP, ASP, Servlet, CGI, PHP, etc.  XQuery programs can accomplish most tasks of other tools aforementioned, and yet is much simpler to learn and easier to write.  Possible direction is to extend XQuery for UPDATE and INSERT to an XML database  Still lack of support from industry till now 29 XML Query Language Tutorial

References  Jonathan Pinnock, et al. “Professional XML, 2nd edition”, ISBN: , WROX Publishers, 2001  Serge Abiteboul, Peter Buneman and Dan Suciu, “Data on the Web: from Relations to Semistructured Data and XML”, ISBN X, Morgan Kaufmann Publishers, 2000  World Wide Web Consortium, “XQuery 1.0. An XML Query Language”, W3C Working Draft, Apr. 30, 2002  World Wide Web Consortium, “XML Path Language (XPath) Version 1.0”, W3C Recommendation, Nov. 16, 1999  Qexo: The GNU Kawa implementation of XQuery,  Don Chamberlin, Jonathan Robie, and Daniela Florescu, “Quilt: An XML Query Language for Heterogeneous Data Sources”, WebDB 2000, Dallas, May XML Query Language Tutorial